Advice on idling problem

Hello All.

I own a 1996 Tacoma with the 2.7 4 cyl.
Its been a great vehicle for 13 years.
Recently it developed what seemed like a miss at idle,
so I had a tuneup done, and fuel systems and ignition check out.
No miss fires found and no OBD codes seen.

Mechanic suspects "balance shaft chain failure".
Vehicle appears to run fine at above idle speeds and
no vibration seems evident. But at idle, the motor shakes
slightly, and imitates a misfire situation. Motor mounts intact.

Mileage is 185000. So, looking for advice as to how to proceed.

As repair cost and year of vehicle are a consideration, looking for
the best solution here.

Thanks to all,

Steve

 

New Tacoma

 

I have the same issue. My truck developed a slightly rough idle and
thwarting sound (th th th th th th th) at idle only, drove smooth otherwise. I thought it was a misfire so I changed plugs, wires, cleaned MAF, new coils, new fuel filter, new PCV valve, sea foamed, and changed to 93 octane. After those changes everything was still the same. So I decided to take it to a mechanic I always use. He hooked these machines to it that gave him real time data and he took it for a couple drives. He found nothing out of the ordinary. While I was there I had him remove and replace a stripped nut on the thermostat housing.

When I got home that evening I took the thermostat housing off and did the jiggle valve mod which on my 3.4 the manual states the jiggle valve needs to be in the downward (6:00) position. After doing that my temps went from 208 down to 190. The other positive effects it had were that the "thwarting" sound went away, power was restored, and it seemed my idle had smoothed out. After a couple more days of driving I could tell the slightly rough idle was still there but for some reason not nearly as noticeable. Now my idle is better but still not as smooth as it should be so I'm still trying to figure that out.

Do you know what your mechanic meant by "Balance Shaft Chain Failure"?
Does that have to do with your timing chain since your a 4cyl?
I have the V6 so its a timing belt which I had changed maybe 7 months ago. I wonder if the harmonic balancer/ pulley would be something to check?

Have you checked for exhaust leaks?

I'm at a loss for what else to check.